It's happened more times than you care to remember. You're sitting at your PC, putting the final period on that four-page e-mail, and your foot catches the system's power cord, yanking it from the socket. The e-mail is lost forever, and before you can start retyping it, you have to wait several minutes for the machine to boot, cursing yourself as Windows lets out that lingering chime.

Such horror stories could soon be a thing of the past, thanks to magnetoresistive random access memory, or MRAM for short. By the middle of the decade, manufacturers expect to start building PCs with MRAM. If an MRAM computer loses power, you can restart it in an instant, and when you do, that four-page e-mail will be right where you left it.

Today's PCs use SRAM (static RAM) and DRAM (dynamic RAM), both known as volatile memory. They can store information only if they have power. DRAM is a series of capacitors that store information as electrical charges. A charged capacitor represents a 1, and an uncharged capacitor represents a 0.

To retain a 1, you must constantly feed the capacitor with power. "The charges you put into a capacitor are constantly leaking out," says Chia-Ling Chien, a professor of physics in the Krieger School of Arts and Sciences at Johns Hopkins University, whose research has long focused on magnetic structures. "Several thousand times a second, you have to replenish them, or they go away."

That's why when you pull the plug on your PC, everything stored in memory vanishes. Work that hasn't been saved to your hard drive can never be retrieved. And when you turn the system back on, it has to reload the entire operating system.

Gestating in research labs for decades, MRAM stores bits as magnetic polarities rather than electrical charges. MRAM bits are made from magnetized metal material. When a bit's polarity points in one direction, it holds a 1. When its polarity points in another direction, it holds a 0. The bits need electricity to change polarities but not to maintain them. MRAM is nonvolatile, so when you turn off the power, all the bits retain their 1's and 0's.

"If MRAM replaces DRAM, then you don't have to worry when your computer crashes and you haven't saved what you're working on to your hard drive," says Chien. "Everything stays in memory." And you don't have to reload the operating system, which stays in memory, letting you restart your system instantly.

MRAM will probably debut around 2004. In June 2002, Motorola demonstrated the first 1-megabit MRAM chip. Hewlett-Packard and IBM are also working on the technology. But it could be a while before MRAM is in every PC, because manufacturers are set up to build DRAM, and replacing the infrastructure takes time and money. "Any time you move away from pure silicon, there are going to be problems that are very difficult to get past," says Jim Handy, an analyst with market research firm Semico Research. He says MRAM won't replace DRAM for another 10 to 20 years.

MRAM could let developers reinvent other parts of a PC as well. Potentially much faster than the continuous magnetic media inside today's hard drives, it may lead to better mass storage devices. And it may be the catalyst for a new breed of microprocessor that PC manufacturers can customize. "Today, every AND gate, every OR gate, is burned onto a processor and can't be changed," says Chien, referring to a chip's logic architecture. "The hope is that MRAM will one day be mature enough for programmable logic, so you could build two identical chips and later reconfigure them to do completely different things."

But that's just icing on the cake. The real news is that you won't have to worry about your feet catching that power cord.

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